The objective of this study is to determine the bioavailability of a polymer coated and buffered UDCA (URSOCARB) as compared to ACTIGALL on percent UDCA enrichment in the bile, proportion and concentration of UDCA in serum, and compare the differences between the results for these two treatments in patients with cystic fibrosis and chronic liver disease. Following a four-week treatment with ACTIGALL at 15-30 mg/kg/day (given in two divided doses), the subjects will have samples of bile (string test), blood and urine collected. The subjects will then have a 24-hour wash-out period, and be switched to URSOCARB at 15-30 mg/kg/day (given in two divided doses). At the end of four weeks of treatment, the subjects will have samples of bile (string test), blood and urine collected. The samples of bile will be analyzed for the degree of UDCA enrichment. Serum and urinary excretion will be measured; enhanced renal output of UDCA will support the contention that greater solubility of UDCA in the intestine increases absorption and bioavailability.